What are GHGs?

Greenhouse gases (also known as GHGs) are gases in the earth’s atmosphere that trap heat and keep the Earth warmer than it would be without them. Some GHGs occur naturally in the atmosphere, while others result from human activities. Naturally occurring GHG’s include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases:

• Water vapor is the most abundant greenhouse gas. It increases as the earth's atmosphere warms but unlike carbon dioxide  which can remain in the earth’s atmosphere for centuries, water vapor persists for only a few days before being cycled out of the atmosphere.
• Carbon dioxide is released to the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned.
• Methane emissions result from the decomposition of organic wastes in municipal solid waste landfills, and the raising of livestock.
• Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels

Greenhouse gases that are not naturally occurring include byproducts of refrigeration, and air conditioning called chlorofluorocarbons (CFCs), as well as hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) generated by industrial processes.

How do GHGs trap heat?

The reason they warm the Earth has to do with the way energy enters and leaves our atmosphere. The gases act like the glass walls of a greenhouse – hence the name, greenhouse gases. When energy from the sun first reaches us, it does so mainly as light. But when that same energy leaves the Earth, it does so as infrared radiation, which we experience as heat. Greenhouse gases reflect infrared radiation, so some of the heat leaving the Earth is absorbed and re-emitted by the greenhouse gases in our atmosphere and comes back to the Earth’s surface.

The greenhouse effect is not a bad thing. Without it, our planet would be too cold for life as we know it. But as the amount of greenhouse gases in the atmosphere changes, the strength of the greenhouse effect changes too. This is the cause of human-made climate change: by adding greenhouse gases to the atmosphere, we are trapping more heat, and the entire planet gets warmer.

How does Carbon effect climate change?

For climate change, the most important greenhouse gas is carbon dioxide, which is why you hear so many references to “carbon” when people talk about climate change. There are three main reasons CO2 is so central to the global warming happening today. First, there is just so much of it: we now add over 35 billion tons of CO2 to the atmosphere every year, mostly by burning carbon-rich fuel like coal and oil that had previously been trapped in the ground. Second, it lasts a long time in the atmosphere. The CO2 emitted today will continue absorbing and re-emitting heat for hundreds of years. This means that, even if all new CO2 emissions stopped tomorrow, it will take many lifetimes before the warming effect of our past emissions fades away.

Finally, many different industries rely on carbon-rich fuels or other processes that give off CO2. That includes burning fossil fuels for electricity and heat and to power our vehicles. It also includes manufacturing concrete and steel, the refining process for raw oil and gas, fermentation (for instance, to make alcohol or pharmaceuticals), and the decay of plant matter (like after trees are cut down). While all of these sectors can make changes to emit less CO2, the same solutions won’t work for all of them.

What impact do GHGs have on "good" Ozone?

While greenhouse gases primarily affect Earth's lower atmosphere, they can indirectly impact the ozone layer in the stratosphere. One way they do this is by altering atmospheric circulation patterns, which can, in turn, affect the distribution of ozone. Additionally, some greenhouse gases, such as chlorofluorocarbons (CFCs), have direct ozone-depleting properties in the stratosphere.